How do I phrase this condition in T-SQL syntax? - sql

Question

I have a table in SQL Server 2012 with employees data. An extract is shown below:
empID DateOfEntry DateLeft
102 2015-05-21 2016-04-20
104 2015-05-14 2015-12-28
...
I need to extract all employees who were present during the period 2016-07-01 and 2017-06-30.
To do this, I need to add a WHERE filter on the DateLeft column in my query but I am a bit confused as to how to phrase this logic.

Answer 1

I think this is what you are after:
WHERE DateOfEntry <= '2017-06-30'
and DateLeft >= '2016-07-01'
You can think of your question as "people who started before (or on) your latest date and left after (or on) your Earliest date".

Answer 2

"all employees who were present during the period 2016-07-01 and 2017-06-30"
Your phrasing implies several scenarios so I will address all
If you want employees who were present in these two dates specifically, use IN operator in your where filter:
SELECT *
FROM <Table>
WHERE DateLeft in ('2016-07-01','2017-06-30');
If you want employees who were present through these range of two dates you can use
'between' syntax:
SELECT *
FROM <Table>
WHERE DateLeft between '2017-06-30' and '2016-07-01';
Note that when using 'between' begin and end values are included, so assuming you want to exclude the last date in range for example you will need to use greater then or equal / lower then operators
SELECT *
FROM <Table>
WHERE DateLeft >= '2017-06-30' and DateLeft < '2016-07-01';

Answer 3

I think you need something like this.
DECLARE #Employee TABLE(empID INT,DateOfEntry DATE,DateLeft DATE)
INSERT #Employee
SELECT 101,'2015-05-21','2016-08-20' UNION ALL -- O
SELECT 102,'2015-05-21','2016-04-20' UNION ALL -- X
SELECT 104,'2015-05-14','2015-12-28' UNION ALL -- X
SELECT 105,'2015-05-14','2018-12-28' -- O
DECLARE #StartDate DATE = '2016-07-01'
DECLARE #EndDate DATE = '2017-06-30'
SELECT * FROM #Employee
WHERE
(DATEDIFF(DAY,DateLeft,#StartDate) <=0 AND DATEDIFF(DAY,DateLeft,#EndDate) >= 0)
OR
(DATEDIFF(DAY,DateLeft,#StartDate) <=0 AND DATEDIFF(DAY,DateLeft,#EndDate) <= 0)

Answer 4

Try this:
SELECT *
FROM [mytable]
WHERE [DateOfEntry] >= '2016-07-01'
AND [DateLeft] <= '2017-06-30';
Also, when working with dates and ranges, do not use BETWEEN even some people are going to show you the syntax.
To be precise, you should avoid passing dates as string in this format, too:
YYYY-MM-DD
As it can break under certain scenarios — such as when the user's language settings are set to French:
SET LANGUAGE FRENCH;
GO
SELECT CONVERT(DATETIME, '2009-10-13');
You can use YYYYMMDD instead.
Aaron Bertrand has nice article about dates and dates ranges, part of his series - Bad habits to kick - you can find more details and examples there, if you want :-)